ACTIVE CONTROL OF VORTEX SHEDDING IN THE FAR WAKE OF A CYLINDER

Abstract eng:
In this paper, some preliminary results reported from experimental observations of two-dimensional air flows with a Reynolds number of 170 passing a stationary circular cylinder and its active control achieved in the far wake. The free stream velocity of the wind tunnel maintained uniformly at U∞=80.4 cm/sec during the experiment. The amplitude of velocity fluctuations measured vertically above the cylinder centerline with a hot-wire probe positioned at a streamwise station of x/d=7 (far wake) on center under natural and control conditions of the transitional flow in the wake of the cylinder. The feedback hot-wire sensor was located in the upper shear layer of the cylinder at about 0.9d streamwise and about 0.8d above the cylinder axis. After the phase of the feedback signal shifted 180˚±2˚ and the amplifier gain adjusted, perturbations imposed at vortex-shedding frequency on the wake of the cylinder on both sides of the wind tunnel. The induced perturbations were significant and the Karman vortex street responded vigorously to the feedback of the signal from the hot-wire sensor in the wake of the cylinder at vortex-shedding frequency. The power spectrum of turbulence velocity fluctuations significantly reduced at Strouhal frequency. This is interpreted as the control of vortex shedding achieved in the far wake of a cylinder. Thereafter, the amplitudes of velocity fluctuations were significantly reduced in the Karman vortex street. In this experiment, we have been able to demonstrate the active of vortex shedding in the beginning of the far wake distance x/d=7 of the cylinder-wake at Strouhal vortex shedding frequency, However, shedding of the vortices in the wake not controllable at distance x/d = 20 and further downstream.

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